首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   150257篇
  免费   8517篇
  国内免费   130篇
林业   7219篇
农学   5238篇
基础科学   1003篇
  20655篇
综合类   19578篇
农作物   6015篇
水产渔业   8517篇
畜牧兽医   78267篇
园艺   2170篇
植物保护   10242篇
  2021年   1243篇
  2020年   1419篇
  2019年   1664篇
  2018年   2748篇
  2017年   3082篇
  2016年   2855篇
  2015年   2486篇
  2014年   2967篇
  2013年   6420篇
  2012年   5356篇
  2011年   6086篇
  2010年   3980篇
  2009年   3952篇
  2008年   5726篇
  2007年   5488篇
  2006年   5074篇
  2005年   5387篇
  2004年   5108篇
  2003年   4932篇
  2002年   4163篇
  2001年   4971篇
  2000年   4792篇
  1999年   3920篇
  1998年   1509篇
  1997年   1497篇
  1996年   1372篇
  1995年   1641篇
  1994年   1354篇
  1993年   1379篇
  1992年   2872篇
  1991年   3034篇
  1990年   2990篇
  1989年   2996篇
  1988年   2748篇
  1987年   2710篇
  1986年   2664篇
  1985年   2526篇
  1984年   2035篇
  1983年   1788篇
  1982年   1189篇
  1979年   1767篇
  1978年   1377篇
  1977年   1230篇
  1975年   1270篇
  1974年   1473篇
  1973年   1575篇
  1972年   1514篇
  1971年   1320篇
  1970年   1324篇
  1969年   1238篇
排序方式: 共有10000条查询结果,搜索用时 812 毫秒
901.
902.
903.
904.
905.
906.
907.
Although most of the magnetic flux observed on the sun originates in the low-latitude sunspot belts, this flux is gradually dispersed over a much wider range of latitudes by supergranular convective motions and meridional circulation. Numerical simulations show how these transport processes interact over the 11-year sunspot cycle to produce a strong "topknot" polar field, whose existence near sunspot minimum is suggested by the observed strength of the interplanetary magnetic field and by the observed areal extent of polar coronal holes. The required rates of diffusion and flow are consistent with the decay rates of active regions and with the rotational properties of the large-scale solar magnetic field.  相似文献   
908.
Alleviation of postanesthetic hypoxemia in the horse   总被引:1,自引:0,他引:1       下载免费PDF全文
This study was designed to investigate the effect of the nasotracheal insufflation of oxygen at a flow rate of 15 L/min on the arterial partial pressure of oxygen during the recovery period following inhalation anesthesia in the horse. It has been stated that this is a suitable flow rate to prevent postoperative hypoxemia but without any experimental evidence to support those statements. Horses being used for the study of healing of cartilage were anesthetized on two separate occasions. Following one period of anesthesia they were allowed to recover breathing room air, and following the other period of anesthesia oxygen was insufflated into the trachea at 15 L/min throughout the recovery period. This permitted each horse to act as its own control and allowed statistical analysis using Student's t-test for paired samples.

The insufflated horses had a higher arterial partial pressure of oxygen during the recovery period than did the noninsufflated horses (p < 0.05).

  相似文献   
909.
Atrophic rhinitis is caused by toxigenic Pasteurella multocida strains. The infection is supported by Bordetella bronchiseptica and other widespread agents and by non-infectious factors damaging the nasal epithelium. The term "infectious multifactorial disease" means in German, that ubiquitous low-virulent agents cause disease when intensified by non-infectious factors. Atrophic rhinitis does not belong to this group but is an infectious disease, caused by a specific agent and influenced by several factors.  相似文献   
910.
1. One hundred and twenty (60 male and 60 female) 21‐d‐old Ross 1 broiler chicks were reared in cages in rooms kept at 21°C or 31°C and were killed at body weights of 1.0, 1.5, 2.0, 2.5 or 3.0 kg.

2. Birds reared at either of the two temperatures ate similar quantities of food to reach their slaughter weight although at 31°C they took longer to reach it.

3. The meat yields of the birds at each slaughter weight were similar at both rearing temperatures, but at body weights greater than 2.0 kg, the broilers reared at 21 °C had more breast meat than those reared at 31°C.

4. Females ate more food than males to reach each of the slaughter weights. The females deposited more fat and had a greater skin weight than the males and, although they had a similar amount of total meat, they had more breast meat.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号